Hallucinations | Oliver Sacks

Summary of: Hallucinations
By: Oliver Sacks


Dive into a fascinating exploration of the human mind in the book ‘Hallucinations’ by Oliver Sacks. In this summary, you will discover how hallucinations occur, spanning a range of scenarios from Charles Bonnet Syndrome in people with visual impairments to the impact of sensory deprivation on our perception. Understand the roles of neurological conditions such as Parkinson’s and Alzheimer’s in hallucinations, and learn about the effects of psychedelic drugs and migraines on our interpretations of reality. Additionally, gain insights on how sleep disorders and emotional states, such as grief and post-traumatic stress disorder, can cause hallucinatory experiences.

Hallucinations and the Brain

Perception vs Reality: The Science Behind Visual Hallucinations

Hallucinations are a common phenomenon experienced by many, especially those who are blind or visually impaired. This is known as the Charles Bonnet Syndrome (CBS) and was first described in 1760 by a Genevan naturalist named Charles Bonnet. The CBS hallucinations are so vivid and realistic that patients often mistake them for reality. This happens because the hallucinations come from the same areas of the brain as visual perception. In fact, a study shows that almost 90% of elderly people with visual problems experience some form of hallucinations.

Additionally, sensory deprivation can also lead to visual hallucinations. When a person is exposed to the same monotonous scene, such as darkness, for an extended period, their brain creates visions, ranging from simple patterns to complex scenes. This phenomenon is known as the prisoner’s cinema.

Therefore, what one perceives may not always be reality. The brain processes sensory information and creates perceptions that may or may not correspond to external reality. The science behind visual hallucinations helps us understand that the brain is a complex organ that requires further exploration.

Smell and Sound Hallucinations

Smell and sound hallucinations are more common than most people think. Losing the sense of smell completely, also called anosmia, affects about five percent of people. Losing some parts of it leads to sensory distortions, called dysosmia. Perfume, coffee and cars might smell unbearably strong to those with dysosmia. Also, dysosmia affects people’s sense of taste, making them taste metallic and rotten. Auditory hallucinations are also widely spread, and most people who hear voices are not suffering from severe mental disorders. Hearing your own name is the most common auditory hallucination. Breaching the barrier that prevents us from hearing our own internal voices is a possible explanation for hallucinating unremarkable voices.

Hallucinations in Degenerative Diseases

Parkinson’s disease is a degenerative disease that affects many people and causes shaky, rigid, and slow movements. Researchers later discovered that over a third of those affected also experienced hallucinations. Degenerative diseases, including Alzheimer’s disease, often result in complex and multi-sensory hallucinations. L-dopa is a drug that is used to treat Parkinson’s disease by heightening dopamine responsiveness, which can lead to hallucinations similar to LSD. People with Parkinson’s who experience hallucinations like these don’t always consider them bad, with some reporting their hallucinations are fascinating and enjoyable. Other forms of dementia like Alzheimer’s disease also cause hallucinations, often involving disorientation, confusion, and delusions. Patients may imagine that people or things around them have changed in some way. In conclusion, as we age and suffer from degenerative diseases, the likelihood of experiencing hallucinations increases.

Phantom Limbs and Other Body Hallucinations

The phenomenon of phantom limbs, where an amputee feels as if the amputated limb is still attached to their body, is a common experience. Neurologist Silas Weir Mitchell coined the term in 1870 and it is a unique form of hallucination that appears almost immediately after amputation. People with phantom limbs feel that they are a regular part of their body and can move them voluntarily. This kind of hallucination is distinct from other hallucinations associated with sensory impairment. In some cases, amputees can still use their phantom limb, as seen in the case of pianist Paul Wittgenstein who continued to teach piano with his left stump. The article also explores other body hallucinations, such as doubles or shadows that are even stranger than phantom limbs. One man who had to undergo parietal lobe surgery believed that someone had left a dead, cold leg in his bed, when in fact it was his own, still attached.

The Science of Psychedelics

Psychedelic drugs have different effects on the brain, including vivid hallucinations and stimulation of complex brain functions. This summary highlights some of the psychoactive substances found in plants and labs, their effects, and how they contribute to better understanding the brain’s neurological complexities.

Psychedelic drugs have been used by many people to achieve specific experiences, including intense feelings of pleasure and euphoria. Mescaline, found in some cactuses, causes hallucinations of complicated geometrical patterns while psilocybin, present in many mushrooms, can lead to delightful colorful visual experiences. In 1938, Schultes and Hofmann documented the catalog of nearly one-hundred plants containing psychoactive substances in Plants of the Gods. As research in the field continued, scientists discovered mightier chemicals that can stimulate complex functions in the brain.

Delirium, or the experiencing of hallucinations from alcohol toxicity, withdrawal or other common causes such as fever, can lead to the Alice-in-Wonderland syndrome, a condition where people imagine their body is growing or shrinking, resulting in rhythmic and pulsing visual hallucinations. Dr. Sacks acquainted himself with psychedelic drugs, particularly LSD, to gain better insight into the neurological complexities of the brain.

In summary, this insightful excerpt highlights some significant aspects of the science of psychedelics – their positive and negative effects on the brain, and how they contribute to our understanding of the human nervous system.

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